feat: Slice 1 polish - MiMo V2.5 model, visible reasoning, image attachments, mobile keyboard fix

- Switch conversation agent to xiaomi/mimo-v2.5 (multimodal: text + image)
- Render native reasoning parts as live 'Thinking trace' (streaming open,
  collapsed after completion); inline <think> extraction for streaming models
- Image attachments: picker (up to 4, 10MB each), base64 to Flue
  AgentPromptImage, authenticated blob-URL replay for historical images
- Mobile keyboard viewport fix: visual-viewport hook, fixed shell,
  interactive-widget=resizes-content, header pinned, composer follows keyboard
- Conversation to Signal to proposed Work: Convex persistence, Effect
  validation in @code/work-os, Work cards with exact source provenance
- Streamdown markdown + Mermaid chart rendering in chat messages
- Flue tool turns hidden, reasoning-containing turns remain visible
- Frontend regression tests: keyboard viewport, responsive shell,
  attachment overflow, authenticated images, reasoning traces, transforms
- .env.example updated to xiaomi/mimo-v2.5 config

docs/README.md

@@ -0,0 +1,57 @@
+# Zopu Work OS — Documentation Map
+
+Dense context set for product development and coding agents.
+
+## Read order
+
+```text
+1. agent-context.md  — bootstrap and non-negotiables
+2. product.md        — product model and quality doctrine
+3. glossary.md       — canonical terminology
+4. dev-loop.md       — normative software delivery process
+5. tech.md           — architecture, actors, ports, runtimes
+6. design.md         — user experience
+7. slices.md         — sequential vertical product increments
+8. dev-plan.md       — repository execution plan/backlog
+9. evaluation.md     — quality measurement and improvement
+```
+
+## Use by role
+
+| Role | Minimum context |
+|---|---|
+| Product/definition agent | agent-context, product, glossary, dev-loop |
+| Architecture/design agent | agent-context, tech, dev-loop, current Work Definition |
+| Coding agent | agent-context, current Design Packet/Slice, tech sections, repository rules |
+| Verifier | agent-context, dev-loop, evaluation, Verification Plan |
+| Frontend agent | agent-context, design, product, current slice |
+| Lead/orchestrator | all documents, current repository state, active decisions |
+
+## Document boundaries
+
+```text
+product.md      what/why
+tech.md         system architecture
+design.md       interaction behavior
+dev-loop.md     how software Work is delivered
+slices.md       how Zopu product is incrementally built
+dev-plan.md     engineering order and release gates
+evaluation.md   how quality and improvements are measured
+glossary.md     exact term definitions
+agent-context   compact instructions for execution agents
+```
+
+## First build target
+
+```text
+message
+→ Signal
+→ approved Work Definition
+→ approved Design Packet
+→ one isolated implementation slice
+→ independent verification
+→ exact verified PR
+→ human question/resume
+```
+
+Start at `dev-plan.md` backlog item 01. Do not begin dynamic Kit Builder or fleets before Slices 1–7 work reliably.